Elastic-Damaging Plasticity Model for Ductile Fracture

Abstract

This study is directed toward the development of a simple material model that can characterize ductile fracture in ferritic steels and that can be used in practical engineering problems. Ductile fracture occurs by a sequential process of nucleation, growth and coalescence of microvoids or microcracks. However, the model uses a continuum approach that can capture the global effect of ductile fracture behavior. It consists of two uncoupled material models; an elastic-damaging model that employs continuum damage mechanics and a von Mises plasticity model. The elastic-damaging model is based on the assumption that damage occurs due only to hydrostatic tension, and this, combined with the von Mises plasticity model, allows a simple formulation of the proposed model. Parameters required by the proposed model are determined by calibrating against experimental data for a specific material. The parameters for the elastic-damaging model depend on the spatial distribution of hydrostatic tension, and are determined by a calibration procedure that utilizes axisymmetric notched specimens. The proposed model is implemented in ABAQUS using a user-defined subroutine, i.e. UMAT. Applications to four-point plane strain bending specimens with a key hole notch and to double-tee circular hollow section tubular joints are presented. The proposed model appears to be capable of simulating, with reasonable accuracy, the failure of metal structures due to ductile fracture.